1. Field of the Invention
The present invention relates to locating objects.
2. Description of the Related Art
A new class of products is emerging in the marketplace. These systems are designed to track small, low-powered radio beacons that are attached to assets and personnel in a facility. The radio beacons are generally called xe2x80x9ctagsxe2x80x9d. The tags can be read at relatively long range, typically in excess of 50 meters. Antennas are installed indoors or outdoors in a grid-like fashion to cover a complete facility. The antennas remain in continuous contact with tags in range of the antennas.
Systems of this type are known as xe2x80x9cLocal Positioning Systemsxe2x80x9d (LPS), xe2x80x9cReal Time Locating Systemsxe2x80x9d (RTLS), or xe2x80x9cLocal Locating Systemsxe2x80x9d (LLS). All of these names emphasize the ability of the systems to cover a complete indoor space (as distinct from covering gateways or portals), read tags from long distances, and determine tag locations. The term LPS indicates that techniques similar to Global Positioning System (GPS) techniques are used to determine tag location. Other RTLS technologies estimate location based on reader proximity and/or signal strength. RTLS systems as a group are distinguished from Radio Frequency Identification (RFID) in that RFID systems are designed to see tags at short range only, and catch them as they pass fixed points in a constrained process.
Referring to FIG. 1, Local Positioning Systems (LPS) are designed to track small, low-powered radio beacons that are attached to assets and personnel in a facility. One commercially available LPS is PinPoint""s 3D-iD system, available from PinPoint Corporation, 1 Fortune Drive, Billerica, Mass. 01821. 3D-iD is comprised of two main components, shown in FIG. 1, a multi-antenna 102a-102d interrogator 101 that sends Direct Sequence Spread Spectrum interrogation signals 110 at 2.44 GHz to tags 103 (only one shown) that are in range. The tags transpond this interrogation signal, by receiving the signal at 2.44 GHz, mixing the carrier up to 5.80 GHz, filtering the result to comply with regulatory requirements, and transmitting a resulting FCC-compliant signal 112 at low power in the 5.80 GHz band. Interrogator 101 receives this resulting signal, extracts the tag""s unique ID, and determines the tag""s distance to each antenna by measuring the signal""s time of arrival. By comparing the time of arrival with the time of transmission, round trip time of flight is estimated and the distance between the tag and the antenna accordingly is estimated. Information from the interrogator is sent to a host computer 105 (host) using a TCP/IP protocol, typically via an Ethernet connection 104. The host calculates the tag""s location, and makes the information available to application programs. Other implementations of LPS have been designed; some of which are commercially available, such as, FireFly from it is to be understood that all such LPS systems share a requirement to install a matrix of interrogation points in order to read tags in range and determine their locations. However, there is a need for a system that can locate objects located outside of such area of coverage.
One embodiment of the invention is directed to an object locating system utilizing GPS including a tag, attached to the object, and a base station, having a host. The tag includes GPS circuitry, wireless LAN circuitry enabling communication between the host and the tag, and a power-saving feature. The power saving feature may take on numerous forms.
Another embodiment of the invention is directed to a locating system for use in an application including at least one mobile vehicle and at least one mobile object. The locating system comprises: a base station on the vehicle, the base station including a differential GPS receiver; and a tag attached to the object. The tag includes: GPS circuitry; and wireless LAN circuitry for communicating information between the tag and the base station. Inverted differential GPS corrections are performed at the base station on tag positional information. The object may be an individual (person).
An even further embodiment of the invention is directed to a location system for use in an application including at least one mobile object. The location system comprises: a host; and a tag placed on the object. The tag includes: GPS circuitry; inertial technology circuitry; and wireless LAN circuitry for communicating information between the tag and the host. When the tag loses communication with Navstar GPS satellites, the tag utilizes inertial technology to estimate its location as an offset to the last known GPS-based location. The object may be an individual.